The mitochondrion is a complex organelle that plays a key role in carrying out the reactions of energy metabolism. This organelle also performs additional functions crucial for normal cellular growth and development. At least one essential phospholipid biosynthetic enzyme is found only in the mitochondrion. Furthermore, aberrant mitochondrial function and morphology have been implicated in processes leading to cellular senescence and oncogenesis. Finally, mitochondrial phospholipids appear to be involved in the induciton of membrane tolerance following alcohol ingestion. The study of mitochondrial membrane biogenesis may therefore be expected to contribute to an understanding of the role played by the mitochondrion in normal cellular function. This proposal describes an analysis of mitochondrial membrane biogenesis in the model eukaryote yeast. Yeast provides an experimental system which is more easily manipulable from genetic, molecular, and biochemical standpoints than any other eukaryote system. The aim of this proposal is to study the regulation of synthesis of the phospholipid cardiolipin, which is found only in the mitochondrial membrane and can therefore serve as a marker for the study of mitochondrion-specific membrane biogenesis. Three approaches are described; (1) A biochemical characterization of the enzymes which carry out cardiolipin synthesis, and an analysis of the factors which regulate expression of these enzymes will be undertaken. (2) Genetic methods will be employed to characterize cardiolipin mutants recently identified, and also to isolate additional mutants of cardiolipin synthesis. (3) Molecular mechanisms underlying the regulation of cardiolipin synthesis will be studied by cloning the structural genes for cardiolipin biosynthetic enzymes, analyzing expression of mRNAs encoded by these genes, and identifying interactions between regulatory proteins and structural genes. The long term goal of this study is to elucidate the mechanisms whereby eukaryotic cells regulate the biogenesis and function of the mitochondrion. An understanding of mitochondrial function is expected to have far reaching implications for many important physiological processes in eukaryotes.